When it comes to tracking weight loss, most of us rely on the scale to tell us whether we've lost or gained weight. But, as people are fast learning, this isn't the best way to keep track of your weight. A scale measures everything including muscle, fat, bones, and what you ate or drank that day. It doesn't tell you what you really need to know: how much fat do you have?
Body composition is simply the ratio of lean body mass to fat body mass. Too much fat can lead to health problems like heart disease, diabetes, high cholesterol and other serious conditions. If you keep your body fat within a reasonable level, you'll be healthier and, of course, slimmer.

For women, an acceptable percentage is between 25 - 31%.

For men, it's 18 - 25%. Any number over that is considered obese. So, how do you find out what your body fat is? Below are the most popular methods for testing body composition.

• DEXA uses a whole body scanner and two different low-dose x-rays to read bone mass and soft tissue mass.
• It takes about 10-20 minutes to do a body scan
• It provides a high degree of precision with a 2-3 % margin of error.
• This is considered a gold standard for measuring body fat and bone density
• It's painless

• You sit on a scale inside a tank of water and blow out as much air as you can
• You are dunked underwater, where you blow out even more air
• Since fat is lighter than water, the more fat you have, the more you'll float. The scale measures underwater weight to figure out body density.
• The margin of error is around 2-3%, but the accuracy depends on the amount of air you expel. You have to blow it ALL out or it won't be as accurate.
• This is a difficult way to measure body fat since it can be uncomfortable and even scary to be dunked underwater with no air in the old lungs.